CVE-2021-45936 in wolfMQTT
Summary
by MITRE • 01/01/2022
wolfSSL wolfMQTT 1.9 has a heap-based buffer overflow in MqttDecode_Disconnect (called from MqttClient_DecodePacket and MqttClient_WaitType).
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Analysis
by VulDB Data Team • 01/05/2022
The vulnerability identified as CVE-2021-45936 represents a critical heap-based buffer overflow within the wolfSSL wolfMQTT library version 1.9. This flaw exists in the MqttDecode_Disconnect function which is invoked by both MqttClient_DecodePacket and MqttClient_WaitType operations. The issue stems from insufficient input validation and boundary checking during the processing of MQTT disconnect packets, creating a scenario where maliciously crafted data can cause memory corruption. The vulnerability manifests when the library attempts to decode disconnect messages without properly validating the length of incoming data, allowing an attacker to write beyond allocated buffer boundaries. This type of vulnerability falls under CWE-121, heap-based buffer overflow, which is classified as a serious memory safety issue that can lead to arbitrary code execution or system crashes.
The operational impact of this vulnerability is significant within environments that utilize wolfMQTT for MQTT protocol communication, particularly in IoT deployments, industrial control systems, and embedded applications where wolfSSL is integrated for secure messaging. Attackers could exploit this flaw by sending specially crafted disconnect packets to vulnerable systems, potentially leading to denial of service conditions or remote code execution depending on the system configuration and memory layout. The vulnerability affects the MQTT client functionality specifically during packet decoding operations, making it particularly dangerous in scenarios where the client receives untrusted network input. Systems running wolfMQTT 1.9 and earlier versions are at risk, especially in environments where MQTT brokers communicate with numerous clients and the disconnect handling mechanism is frequently invoked. The attack surface expands when considering that MQTT protocol is widely used in smart grid systems, automotive applications, and industrial automation where reliability and security are paramount.
Mitigation strategies for CVE-2021-45936 should prioritize immediate patching of the wolfSSL wolfMQTT library to version 1.9.1 or later, which contains the necessary fixes for the buffer overflow vulnerability. Organizations should implement network segmentation and access controls to limit exposure of MQTT clients to untrusted networks, reducing the attack surface for potential exploitation. Input validation should be strengthened at all levels of the MQTT communication stack, with additional monitoring and logging of disconnect packet handling to detect anomalous behavior. Security teams should conduct comprehensive vulnerability assessments of all systems utilizing wolfMQTT to identify potential exposure and implement proper memory safety checks in custom MQTT client implementations. The fix addresses the root cause by implementing proper bounds checking in the MqttDecode_Disconnect function, ensuring that buffer allocations are validated against incoming packet data lengths. This vulnerability aligns with ATT&CK technique T1203, Exploitation for Client Execution, as it represents a classic buffer overflow attack vector that can be leveraged for remote code execution in vulnerable environments. Organizations should also consider implementing intrusion detection systems that can identify suspicious MQTT traffic patterns and monitor for potential exploitation attempts targeting this specific vulnerability.